Typically, an elevator control device comprises a control drive system that supplies a prescribed drive power as shown in FIG. 1 and a roped elevator that raises and lowers a passenger cage using the drive power supplied from this control drive system.
This control drive system comprises a commercial AC power source 1, a rectifier circuit 2 that converts the AC power of this commercial AC power source 1 to DC power, a DC capacitor 3 that smoothes the DC power converted by this rectifier circuit 2, an inverter 4 that converts the DC power smoothed by this DC capacitor 3 to AC power of a desired frequency and supplies this to a motor 11, and a drive control unit 5 that performs control such as to supply AC power of a frequency in accordance with the speed instruction from the inverter 4 in accordance with a prescribed speed instruction and the rotational speed of the motor 11, and performs control of a resistance chopper, to be described.
Furthermore, the roped elevator comprises a motor 11, a rope 13 wound around a winding drum 12 that is connected with the rotary shaft of this motor 11, a passenger cage 14 and a balancing weight 15 that are suspended at the respective ends of this rope 13.
With an elevator control device as described above, when the passenger cage 14 is raised in a condition in which it is fully loaded with passengers or lowered in a condition in which it is nearly empty, powered operation (power running or powering) is performed whereby power generated in the sequence commercial AC power source 1→rectifier circuit 2 →DC capacitor 3→inverter 4 is applied to the motor 11. Contrariwise, when the passenger cage 14 is lowered in a condition in which the passenger cage 14 is practically fully loaded with passengers or raised in a condition in which it is close to empty, regenerative operation is performed in which power generated by the motor 11 is returned in the sequence: inverter 4→DC capacitor 3. During such regenerative operation, the power that is returned to the inverter 4 from the motor 11 is blocked by the rectifier circuit 2, so the problem may arise that the voltage on the input side of the inverter is increased, damaging the elements that constitute the rectifier circuit 2 or inverter 4.
Accordingly, conventionally, due to the need to dissipate power matching the increase in voltage produced by regenerated power returning to the inverter from the motor 11 during regenerative operation, a construction was adopted wherein a resistance chopper 18 comprising a self-extinguishing element 16 and resistance 17 was connected across the DC output line of the rectifier circuit 2, so that, if the DC voltage across the DC output line exceeded the set voltage during regenerative operation, a control signal 19 turning the self-extinguishing element 16 on was delivered by the drive control unit 5, causing power matching the increase in voltage to be dissipated by the resistance 17. An example thereof is disclosed in Laid-open Japanese Patent Application No. (Tokkai H. 5-17078).
However, with an elevator control device constructed as described above, there is the problem that the power that is generated by the motor 11 during regenerative operation is dissipated by the resistance 17 as heat, so the power obtained by regenerative operation cannot be effectively utilized.
In view of the above, an object of the present invention is to provide an elevator control device that performs control such that the power produced by regenerative operation is reliably stored and can be effectively utilized during powered operation.